Sunday, February 16, 2014

A NOTE ON ANATOMY OF PAROTID GLAND

Parotid gland


The parotid gland is the largest of the salivary glands.

The parotid, a serous compound tubulo-alveolar gland, is yellowish, lobulated, and irregular in shape.

It occupies the interval between the sternomastoid muscle and the mandible.

Average Wt - 25gm (varies in weight from 14 to 28 gm)



Surface anatomy

The parotid gland lies inferior to the zygomatic arch, anteroinferior to the external acoustic meatus, anterior to the mastoid process, and posterior to the ramus of the mandible.


Relations





The parotid gland is enclosed in a sheath (parotid fascia) and is shaped roughly like an inverted pyramid, with three (or four) sides (fig A).

It has a base (from which the superficial temporal vessels and auriculotemporal nerve emerge),apex (which descends inferior and posterior to the angle of the mandible),and lateral, anterior, and posterior (or posterior and medial) surfaces.
The lateral surface is superficial and contains lymph nodes.

The anterior surface is grooved by the ramus of the mandible and masseter (fig.B), producing a medial lip (from which the maxillary artery emerges) and a lateral lip, under cover of which the parotid duct, branches of the facial nerve, and the transverse facial artery emerge (see fig. C).

The posterior surface is grooved by  the mastoid process and the sternomastoid and digastric muscles and  more medially by the styloid process and its attached muscles.

Medially, the superior part of the gland is pierced by the facial nerve and the inferior part by the external carotid artery.

The following structures lie partly within the parotid gland, from superficial to deep:


1. The facial nerve forms the parotid plexus within the gland and separates the glandular tissue partially into superficial and deep layers ("lobes"). In surgical excision of the parotid gland (e.g., for a tumor), damage to the facial nerve is a possibility.

2. The superficial temporal and maxillary veins unite in the gland to form the retromandibular vein, which contributes in a variable manner to the formation of the external jugular vein (see fig. D).

3. The external carotid artery divides within the parotid gland into the superficial temporal and maxillary arteries.


Parotid duct

The parotid duct is about 7 cm long

The parotid duct, emerging under cover of the lateral surface, runs anteriorward on the masseter and turns medially to pierce the buccinator.

The branching of the duct can be examined radiographically after injection of a radio-opaque medium. 

The parotid duct, which is palpable, opens into the oral cavity on the parotid papilla opposite the upper second molar tooth.

Innervation of parotid gland ( fig. E)




Preganglionic parasympathetic secretomotor fibers (from the glossopharyngeal, tympanic, and lesser petrosal nerves) synapse in the otic ganglion.

Postganglionic fibers travel with the auriculotemporal nerve and so reach the gland.

Cranial nerves VII and IX communicate, so that secretory fibers to each of the three major salivary glands may travel in both the facial and glossopharyngeal nerves.

The sympathetic supply to the salivary glands includes vasomotor fibers.

Blood supply


The arteries supplying the parotid gland are derived from the external carotid, and from the branches given off by that vessel in or near its substance. The veins empty themselves into the external jugular, through some of its tributaries.

Lymphatics


The lymphatics end in the superficial and deep cervical lymph glands, passing in their course through two or three glands, placed on the surface and in the substance of the parotid.




Monday, April 2, 2012

A Note on Anterior cross bite


Anterior cross bite
Possible causes
Class III skeletal pattern

Crowding

Retained primary teeth and roots



Presence of supernumerary teeth

Trauma

Clinical features
  • Instanding maxillary incisor occluding behind the corresponding lower incisors.
  • Over bite which can vary from nothing to excessive depth.
  • Gingival recession of the lower incisor involved.
  • Forward displacement of the  mandible-  instanding tooth comes into premature contact along the normal path of closure.
  •      mobility of the lower incisor involved in the cross bite.

Methods available for correction
Spoon handle biting.
Removable appliance with either cantilever spring or screw.
Lower inclined bite plane.
     
Spoon handle biting
Instruct the child to bite on a spoon handle to guide the incisor which is erupting into cross bite.
 Do not attempt this on an erupted incisor which has a positive over bite.
Once cross bite established,
Identify predisposing factors and remove them to prevent development of the cross bite
Once the cross bite is established, identify and remove aetiological factors responsible and select appropriate method for correction.

Removable appliance
Selection of appliance and the spring design depend on,
      Axial inclination of the tooth

Depth of the over bite.

Amount of forward movement required


Number of teeth involved in the cross bite

Appliance design
Select the best active component which should be used depending on the above factors discussed.
Adequate number of clasps
Add adequate number of clasps to the appliance to resist the reaction of the vertical component of the active force.
Appliance design
Add posterior bite plane to disocclude teeth
Instruction to the technician
Adams clasps on 6/6 d /d
Double cantilever spring(Z spring) on /1
Posterior bite plane (half molar capping)

Management of patient
Fit the appliance and give adequate instructions to the patient to wear it regularly including meal time.
Activate the spring by the correct amount.
Adjust clasps and check the thickness of the molar capping.
Give adequate instruction to the parents as well.
Monitor progress of treatment
If cross bite is corrected and depth of the over bite adequate to ensure the stability of the occlusion discontinue appliance
Monitor the development of the occlusion until the occlusion of the permanent dentition is established.
Incisors cross bite before and after correction

Incisor cross bite not corrected early lead to a severe malocclusion 


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